1. Field of the Invention
The present invention relates to a wireless access system, and more particularly to a method for effectively transmitting and receiving a broadcast channel, and providing a variety of superframe structures and a super frame header structure.
2. Discussion of the Related Art
FIG. 1 is a structural view illustrating an example of a frame structure.
Referring to FIG. 1, one superframe includes one or more frames, and one frame may include one or more subframes. In addition, one subframe may include one or more Orthogonal Frequency Division Multiplexing Access (OFDMA) symbols. The lengths and numbers of superframes, frames, subframes and symbols may be changed according to user requirements or system environments, etc.
An Institute of Electrical and Electronics Engineers (IEEE) 802.16 system or a 3rd Generation Project Partnership 2 (3GPP2) UMB system may have a superframe having the length of 20 ms. In FIG. 1, it is assumed that the length of one superframe is 20 ms and the length of one frame is 5 ms. That is, one superframe may be composed of 4 frames, and one frame may be composed of 8 subframes. At this time, one subframe may be composed of 6 OFDMA symbols.
In FIG. 1, a first subframe of each superframe includes a Super Frame Header (SFH). The SFH may be broadcast to a channel for transmitting system information through the entire cell. The 3GPP system includes a broadcast channel (BCH) serving as a channel similar to the SFH.
A subframe MAP is present in the front part of the subframe contained in the superframe. The subframe MAP may include control information of each subframe.
One or more control channels may be contained in the SFH. Individual control channels may include different information due to a difference in individual transmission purposes, and be transmitted. Preferably, since the SFH and the BCH are transmitted to all cells of the entire network, the SFH and the BCH may be transmitted using the safest method. Therefore, the SFH or the BCH may be coded at the lowest Modulation and Coding Scheme (MCS) level.
However, transmission of all channels contained in SFH or BCH at the lowest MCS level may cause large overhead to a system.